Fracturing and the environment
Ah, common sense. I never really understood why so much oil is left in mature fields. Just to the East of Vienna the Prottes field produces oil since the days of the Empire. Those are old fields and they had been ransacked by the Soviets before they left Austria. Still they are being stimulated to produce more oil. EOR is a good thing and so are all other well stimulation techniques such as fracking. You do it deep undergrond, not at the surface.